Age-Dependent Cerebral Vascular Dysfunction and Neurovascular Coupling Deficits in Col4a1 Mutant Mice ^†

Neurovascular coupling (NVC) is a vital process ensuring that blood flow is rapidly delivered to the most active areas of the brain, supporting the energetic needs of neurons during tasks such as learning, movement, or memory formation. Disruption of this process can reduce the brain’s ability to function correctly and contribute to cognitive decline in aging and in pathologies such as cerebral small vessel disease (cSVD) and Alzheimer’s disease. Capillary-to-arteriole dilation, in which brain capillaries act as sensors of neural activity and trigger upstream blood vessels to dilate, is essential for NVC.

Mutations in COL4A1 cause a hereditary form of cSVD, but the mechanisms by which these mutations impair brain blood flow regulation and cognition during aging remain unclear. In this study, we used a genetically engineered mouse model carrying the Col4a1^+/G394V mutation, which mirrors vascular and cognitive symptoms observed in some patients with COL4A1-related disease. We examined how this mutation affects capillary-to-arteriole dilation, cerebral blood flow, and memory in young adult and aged mice.

We found that young Col4a1^+/G394V mice (3 months old) had normal neurovascular responses and performed well in tests of spatial working memory. In contrast, aged mutant mice (12 months old) showed significant impairments in capillary-to-arteriole dilation, blood flow responses, and had difficulty with memory tasks. Our investigation revealed that the primary defect in older mice was the loss of function in a key ion channel, K_ir2.1 (inwardly rectifying K⁺ channel 2.1), located in brain capillary endothelial cells. These channels detect localized changes in neural activity and initiate the dilation of upstream arterioles. Critically, we discovered that K_ir2.1 channel dysfunction was due to the depletion of the minor membrane phospholipid PIP₂ (phosphatidylinositol 4,5-bisphosphate). PIP₂ is essential for K_ir2.1 channel function, and its loss disrupts capillary-to-arteriole dilation and cerebral blood flow regulation. PIP₂ depletion was caused by overactivity of phosphoinositide 3-kinase (PI3K), an enzyme that converts PIP₂ into PIP₃ (phosphatidylinositol (3, 4, 5)-trisphosphate). Importantly, when we treated aged Col4a1 mutant mice with a PI3K inhibitor, we restored normal K_ir2.1 channel function, improved blood flow regulation in the brain, and rescued the memory impairments observed in these animals. These benefits were observed in acute ex vivo experiments and longitudinal in vivo treatment studies.

Our findings reveal a previously unrecognized mechanism by which COL4A1 mutations lead to age-dependent cerebrovascular dysfunction and cognitive impairment through PI3K-driven loss of PIP₂ and subsequent K_ir2.1 channel dysfunction. Because PI3K inhibitors are already in clinical use for cancer and other conditions, our research provides a compelling rationale for investigating the repurposing of these drugs as potential treatments for COL4A1-associated diseases.